| Re: Issue 30: Inconsistent state tracking on AC prior toDTLSEstablishment | <– Date –> <– Thread –> |
From: Scott Kelly (skelly arubanetworks.com)
|
|
| Date: Wed, 12 Dec 2007 09:17:15 -0800 (PST) | |
We've had a private discussion on this topic off-list, but have not been
able to come to agreement, so I'll make my comments here. I don't think
we should (or need to) introduce these dramatic changes to the document
just prior to last call.
The "problem" we are trying to resolve resulted when someone added
language saying the AC MAY maintain discovery state. This change was
apparently introduced last January. There is no record of working group
or mailing list discussion -- the change just appeared in a document
update.
On Oct 12, Pat posted a comment saying the state machine language
surrounding discovery state is inconsistent. I agree. It was made
inconsistent by the introduction of discovery state to the AC.
In the issue tracker, there is a comment from Charles which must have
been copied from a private email, as I cannot find it in the list
archives. Here is that comment:
----------------------------------------------
It seems to me that to be in any state at all assumes state is being
maintained. Describing a transition from one state to another with
behavior
caveatted with "if state is being maintained" doesn't make any sense to
me.
If we have no state, then we have no state transitions.
IIRC, don't we allow connections that don't do discovery first (it's
been a
while, correct me if I'm wrong)? In which case, DTLS on the AC should
always
be listening, and transition "f" can be simply a WTP transition. The AC
transition would be back to Idle rather than DTLS setup. You could run
discovery as its own subgraph of the AC state machine. If you wanted to
share
state information between the two, you could have an API to do that.
------------------------------------------------
I agree with what Charles says above.
The changes Pat is proposing do not fix the problem - they actually
introduce new problems and confusion. Since we have agreed that the AC
SHOULD NOT maintain discovery state, the discovery-idle-sulking
transitions make no sense in the context of the AC. However, fixing this
does not require separate state machines, or dramatic changes to the
existing state machine.
In draft-08, section 2.3, just below Figure 3, it says "The CAPWAP
protocol state machine, depicted above, is used by both the AC and the
WTP. In cases where states are not shared (i.e. not implemented in one
or the other of the AC or WTP), this is explicitly called out in the
transition descriptions below."
This implies that we just need to make sure the state machine language
around AC discovery processing is clear. We can do this by adopting
three simple changes recommended in Pat's text below (with minor edits):
For Idle-to-Discovery it should say:
AC: This state transition is executed by the AC
when a Discovery Request message is
received. The AC SHOULD respond with a Discovery Response
message (see Section 5.2). The AC SHOULD NOT maintain WTP
state at this point (see Section 12 for more information).
For Discovery to Idle it should say:
AC: This state transition is executed by the AC after processing
a Discovery Request.
For Discovery to Sulking it says:
AC: This is an invalid state transition for the AC.
With these simple changes, the problem is solved.
--Scott
> -----Original Message-----
> From: Pat Calhoun (pacalhou) [mailto:pcalhoun [at] cisco.com]
> Sent: Tuesday, December 04, 2007 3:28 PM
> To: capwap
> Subject: Re: [Capwap] Issue 30: Inconsistent state tracking
> on AC prior toDTLSEstablishment
>
> All,
>
> I wanted to send the new state machine in order to get as many eyes on
> this one as possible. I have done what I believe is a very thorough
> review, but this is a complex state machine. I will also
> include all of
> the state machine text in order to make it simpler to review.
> Note that
> other than the teardown, no changes were made from the join/config
> states on (meaning, only the lower part of the state machine
> figure was
> modified).
>
> Since there is significant text here, I want to provide a
> little bit of
> information on how this now works:
> - The WTP behaves pretty much the same as before, meaning
> that it uses a
> single state context. When a connection attempt fails, the
> state machine
> goes back to the Idle state, unless some counters have hit a
> threshold,
> in which case the state transitions to the Sulking state. As
> before the
> WTP can do the Discovery phase, in which case either state
> (5) or (c) is
> used.
> - The AC now defines two separate threads; Listener and Service. The
> Listener is the main thread that handles the discovery
> messages. Once a
> connection request is received, it spawns a Service thread to
> deal with
> the WTP. You will notice that the new state machine uses numerals when
> it applies either only to the WTP, or to the Listener thread.
> All state
> transitions that use alphabetic, or symbols, is for the Service thread
> or the WTP. The biggest difference in how the state machines work is
> that on the AC, when a connection is being established, and fails, the
> Service thread's state moves back to the DTLS Setup state, not Idle.
> When the error thresholds are hit, the state moves to Sulking - the
> quiet period. You will also notice a new Dead state, which is
> ONLY valid
> for the Service thread, which is where the thread is terminated, and
> resources are freed.
>
> Comments welcomed,
>
> PatC
>
>
> <text>
> 2.3. CAPWAP State Machine Definition
>
> The following state diagram represents the lifecycle of a WTP-AC
> session. Use of DTLS by the CAPWAP protocol results in the
> juxtaposition of two nominally separate yet tightly bound state
> machines. The DTLS and CAPWAP state machines are coupled
> through an
> API consisting of commands (see Section 2.3.2.1) and notifications
> (see Section 2.3.2.2). Certain transitions in the DTLS
> state machine
> are triggered by commands from the CAPWAP state machine, while
> certain transitions in the CAPWAP state machine are triggered by
> notifications from the DTLS state machine.
>
> /-------------------------------------\
> | /-------------------------\|
> | w| ||
> | x+----------+ y +------------+ ||
> | | Run |-->| Reset |-\||
> | +----------+ +------------+ |||
> u| V ^ ^ ^ z|||
> +------------+--------/ | | |||
> | Data Check | /-------/ | |||
> +------------+<-------\ | | |||
> | | | |||
> /------------------+--------\ | |||
> m| t| o| q v r| |||
> +--------+ +-----------+ +--------------+|||
> | Join |---->| Configure | | Image Data ||||
> +--------+ n +-----------+ +--------------+|||
> ^ |l p| s| |||
> | | \-------------------\ | |||
> | \--------------------------------------\| | |||
> \------------------------\ || | |||
> /--------------<----------------+---------------\ || | |||
> | /------------<----------------+-------------\ | || | |||
> | | i |k 8| | vv v vvv
> | | d+----------------+<--+--------------+ +-----------+
> /-|-|---| DTLS Setup | | DTLS Connect |-->| DTLS TD |
> | | | +----------------+e +--------------+ 7 +-----------+
> | | | 6| ^ ^ |f ^ j| ^ |~
> v v v | | | | | | | |
> | | | | | | \-------\ | /----+------/ |
> | | | | | | | | | \---\ |
> | | | v c| 1 |5 2 v |g |h v v
> | | \->+------+-->+------+ +-----------+ +--------+
> | | | Idle | | Disc | | Authorize | | Dead |
> | | +------+<--+------+ +-----------+ +--------+
> | | ^ 0 |3 ^
> | | | | |b
> | |9 |4 | |
> | \->+---------+<------/ |
> \--->| Sulking |----------------------------------/
> +---------+
> a
>
> Figure 3: CAPWAP Integrated State Machine
>
> The CAPWAP protocol state machine, depicted above, is used by both
> the AC and the WTP. In cases where states are not shared (i.e. not
> implemented in one or the other of the AC or WTP), this is
> explicitly
> called out in the transition descriptions below. For every state
>
> defined, only certain messages are permitted to be sent
> and received.
> The CAPWAP control messages definitions specify the
> state(s) in which
> each message is valid.
>
> Since the WTP only communicates with a single AC, it only has a
> single instance of the CAPWAP state machine. The state
> machine works
> differently on the AC since it communicates with many WTPs. The AC
> uses the concept of two threads. Note that the term
> thread used here
> does not necessarily imply that implementers must use
> threads, but it
> is one possible way of implementing the AC's state machine.
>
> Listener Thread - The AC's Listener thread handles the shared
> services, which includes receiving and responding to Discovery
> Requests. The Listener thread handles the common
> tasks, up to the
> DTLS Setup state. The state machine transitions in the above
> figure are represented by numerals.
>
> Service Thread - The AC's Service thread handles the per WTP
> states, and one such thread exists per WTP connection. This
> thread starts during the DTLS Setup state, which is when the
> DTLSListen command is invoked. When created, the Service thread
> inherits a copy of the state machine context from the Listener
> thread. When communication with the WTP is complete,
> the Service
> thread is terminated. The state machine transitions in
> the above
> figure are represented by alphabetic characters (including
> symbols).
>
> 2.3.1. CAPWAP Protocol State Transitions
>
> This section describes the various state transitions, and
> the events
> that cause them. This section does not discuss
> interactions between
> DTLS- and CAPWAP-specific states. Those interactions, and DTLS-
> specific states and transitions, are discussed in Section 2.3.2.
>
> Idle to Discovery (1): This transition occurs once device
> initialization is complete.
>
> WTP: The WTP enters the Discovery state prior to
> transmitting the
> first Discovery Request message (see Section 5.1). Upon
> entering this state, the WTP sets the DiscoveryInterval timer
> (see Section 4.7). The WTP resets the DiscoveryCount counter
> to zero (0) (see Section 4.8). The WTP also clears all
> information from ACs it may have received during a previous
> Discovery phase.
>
> AC: This state transition is executed by the AC's Listener
> thread, and occurs when a Discovery Request message is
> received. The AC SHOULD respond with a Discovery Response
> message (see Section 5.2). The AC SHOULD NOT maintain WTP
> state at this point (see Section 12 for more information).
>
> Discovery to Discovery (2): In the Discovery state, the WTP
> determines which AC to connect to.
>
> WTP: This transition occurs when the DiscoveryInterval timer
> expires. If the WTP is configured with a list of ACs, it
> transmits a Discovery Request message to every AC
> from which it
> has not received a Discovery Response message. For every
> transition to this event, the WTP increments the
> DiscoveryCount
> counter. See Section 5.1 for more information on how the WTP
> knows the ACs to which it should transmit the
> Discovery Request
> messages. The WTP restarts the DiscoveryInterval timer
> whenever it transmits Discovery Request messages.
>
> AC: This is an invalid state transition for the AC.
>
> Discovery to Idle (0): This transition occurs on the AC's Listener
> thread when the Discovery processing is complete.
>
> WTP: This is an invalid state transition for the WTP.
>
> AC: This state transition is executed by the AC's
> Listener thread
> when it has transmitted the Discovery Response, in
> response to
> a Discovery Request.
>
> Discovery to Sulking (3): This transition occurs on a WTP when AC
> Discovery fails.
>
> WTP: The WTP enters this state when the DiscoveryInterval timer
> expires and the DiscoveryCount variable is equal to the
> MaxDiscoveries variable (see Section 4.8). Upon
> entering this
> state, the WTP MUST start the SilentInterval timer. While in
> the Sulking state, all received CAPWAP protocol messages
> received MUST be ignored.
>
> AC: This is an invalid state transition for the AC.
>
> Sulking to Idle (4): This transition occurs on a WTP when it must
> restart the discovery phase.
>
> WTP: The WTP enters this state when the SilentInterval
> timer (see
> Section 4.7) expires. The FailedDTLSSessionCount,
> DiscoveryCount and FailedDTLSAuthFailCount counters are reset
> to zero.
>
> AC: This is an invalid state transition for the AC.
>
> Sulking to Sulking (a): The Sulking state provides the silent
> period, minimizing the possibility for Denial of Service (DoS)
> attacks.
>
> WTP: All packets received from the AC while in the
> sulking state
> are ignored.
>
> AC: All packets receive from the WTP on the AC's
> Service thread,
> while in the sulking state, are ignored.
>
> Sulking to Dead (b): This transition occurs on the AC
> when the quiet
> period expires.
>
> WTP: This is an invalid state transition for the WTP.
>
> AC: The AC enters this state when the SilentInterval timer (see
> Section 4.7) expires. The AC must clean up all resources
> associated with the control plane DTLS session. The
> data plane
> DTLS session is also shutdown, and all resources freed, if a
> DTLS session was established for the data plane. Any timers
> set for the current instance of the state machine are also
> cleared. The AC's Service thread is terminated.
>
> Idle to DTLS Setup (c): This transition occurs to
> establish a secure
> DTLS session with the peer.
>
> WTP: The WTP initiates this transition by invoking the
> DTLSStart
> command, which starts the DTLS session establishment with the
> chosen AC. When the discovery phase is bypassed, it
> is assumed
> the WTP has locally configured ACs.
>
> AC: The AC initiates this transition by invoking the DTLSListen
> command (see Section 2.3.2.1), which informs the DTLS stack
> that it is willing to listen for an incoming
> session. The AC's
> Listener thread forks an instance of the Service
> thread, along
> with a copy of the state context. If the AC had
> maintained WTP
> state information during the Discovery exchange, or through
> some other means that may include static
> configuration of WTPs,
> the AC MAY provide optional qualifiers in the DTLSListen
> command to only accept session requests a specific WTP. Note
> that the AC SHOULD NOT maintain state information based on an
> unsecured Discovery Request message, as this can lead to a
> Denial of Service attack (see Section 12). In such
> instances,
> the AC MUST ensure that this state information is
> freed after a
> period, which is implementation specific.
>
> Discovery to DTLS Setup (5): This transition occurs to establish a
> secure DTLS session with the peer.
>
> WTP: The WTP initiates this transition by invoking the
> DTLSStart
> command (see Section 2.3.2.1), which starts the DTLS session
> establishment with the chosen AC. The decision of
> which AC to
> connect to is the result of the discovery phase, which is
> described in Section 3.3.
>
> AC: This is an invalid state transition for the AC.
>
> DTLS Setup to Idle (6): This transition occurs when the DTLS
> connection setup has failed.
>
> WTP: The WTP initiates this state transition when it receives a
> DTLSEstablishFail notification from DTLS (see
> Section 2.3.2.2),
> and the FailedDTLSSessionCount or the FailedDTLSAuthFailCount
> counter have not reached the value of the
> MaxFailedDTLSSessionRetry variable (see Section 4.8). This
> error notification aborts the secure DTLS session
> establishment. When this notification is received, the
> FailedDTLSSessionCount counter is incremented.
>
> AC: This is an invalid state transition for the AC.
>
> DTLS Setup to Sulking (d): This transition occurs when repeated
> attempts to setup the DTLS connection have failed.
>
> WTP: The WTP enters this state when the
> FailedDTLSSessionCount or
> the FailedDTLSAuthFailCount counter reaches the value of the
> MaxFailedDTLSSessionRetry variable (see Section 4.8). Upon
> entering this state, the WTP MUST start the SilentInterval
> timer. While in the Sulking state, all received CAPWAP and
> DTLS protocol messages received MUST be ignored.
>
> AC: The AC enters this state with the specific WTP when the
> FailedDTLSSessionCount or the FailedDTLSAuthFailCount counter
> reaches MaxFailedDTLSSessionRetry variable (see Section 4.8).
> Upon entering this state, the AC's Service thread MUST start
> the SilentInterval timer, and ignore all CAPWAP and DTLS
> protocol messages received from the WTP. The AC immediately
> transitions the state to Idle.
>
> DTLS Setup to DTLS Setup (e): This transition occurs when the DTLS
> Session failed to be established.
>
> WTP: This is an invalid state transition for the WTP.
>
> AC: The AC initiates this state transition by the
> Service thread
> when it receives a DTLSEstablishFail notification from DTLS
> (see Section 2.3.2.2). This error notification aborts the
> secure DTLS session establishment. When this notification is
> received, the FailedDTLSSessionCount counter is incremented.
>
> DTLS Setup to Authorize (f): This transition occurs when
> an incoming
> DTLS session is being established, and the DTLS stack needs
> authorization to proceed with the session establishment.
>
> WTP: This state transition occurs when the WTP receives the
> DTLSPeerAuthorize notification (see Section 2.3.2.2). Upon
> entering this state, the WTP performs an authorization check
> against the AC credentials. See Section 2.4.4 for more
> information on AC authorization.
>
> AC: This state transition occurs when the AC receives the
> DTLSPeerAuthorize notification (see Section 2.3.2.2). Upon
> entering this state, the AC performs an authorization check
> against the WTP credentials. See Section 2.4.4 for more
> information on WTP authorization.
>
> Authorize to DTLS Connect (g): This transition occurs to
> notify the
> DTLS stack that the session should be established.
>
> WTP: This state transition occurs when the WTP has successfully
> authorized the AC's credentials (see Section 2.4.4). This is
> done by invoking the DTLSAccept DTLS command (see
> Section 2.3.2.1).
>
> AC: This state transition occurs when the AC has successfully
> authorized the WTP's credentials (see Section
> 2.4.4). This is
> done by invoking the DTLSAccept DTLS command (see
> Section 2.3.2.1).
>
> Authorize to DTLS Teardown (h): This transition occurs to
> notify the
> DTLS stack that the session should be aborted.
>
> WTP: This state transition occurs when the WTP was unable to
> authorize the AC, using the AC credentials. The WTP then
> aborts the DTLS session by invoking the DTLSAbortSession
> command (see Section 2.3.2.1).
>
> AC: This state transition occurs when the AC was unable to
> authorize the WTP, using the WTP credentials. The AC then
> aborts the DTLS session by invoking the DTLSAbortSession
> command (see Section 2.3.2.1).
>
> DTLS Connect to DTLS Teardown (7): This transition occurs when the
> DTLS Session failed to be established.
>
> WTP: This state transition occurs when the WTP
> receives either a
> DTLSAborted or DTLSAuthenticateFail notification (see
> Section 2.3.2.2), indicating that the DTLS session was not
> successfully established. When this transition occurs due to
> the DTLSAuthenticateFail notification, the
> FailedDTLSAuthFailCount is incremented, otherwise the
> FailedDTLSSessionCount counter is incremented.
>
> AC: This is an invalid state transition for the AC.
>
> DTLS Connect to DTLS Setup (i): This transition occurs
> when the DTLS
> Session failed to be established.
>
> WTP: This is an invalid state transition for the WTP.
>
> AC: This state transition occurs when the AC receives either a
> DTLSAborted or DTLSAuthenticateFail notification (see
> Section 2.3.2.2), indicating that the DTLS session was not
> successfully established, and both of the
> FailedDTLSAuthFailCount and FailedDTLSSessionCount counters
> have not reached the value of the MaxFailedDTLSSessionRetry
> variable (see Section 4.8).
>
> DTLS Connect to Dead (j): This transition occurs when the DTLS
> Session failed to be established.
>
> WTP: This is an invalid state transition for the WTP.
>
> AC: This state transition occurs when the AC receives either a
> DTLSAborted or DTLSAuthenticateFail notification (see
> Section 2.3.2.2), indicating that the DTLS session was not
> successfully established, and either the
> FailedDTLSAuthFailCount and FailedDTLSSessionCount counters
> have reached the value of the MaxFailedDTLSSessionRetry
> variable (see Section 4.8).
>
> DTLS Connect to Join (k): This transition occurs when the DTLS
> Session is successfully established.
>
> WTP: This state transition occurs when the WTP receives the
> DTLSEstablished notification (see Section 2.3.2.2),
> indicating
> that the DTLS session was successfully established.
> When this
> notification is received, the FailedDTLSSessionCount
> counter is
> set to zero.
>
> AC: This state transition occurs when the AC receives the
> DTLSEstablished notification (see Section 2.3.2.2),
> indicating
> that the DTLS session was successfully established.
> When this
> notification is received, the FailedDTLSSessionCount
> counter is
> set to zero, and the WaitJoin timer is started (see
> Section 4.7).
>
> Join to DTLS Teardown (l): This transition occurs when the join
> process failed.
>
> WTP: This state transition occurs when the WTP receives a Join
> Response message with a Result Code message element
> containing
> an error, if the Image Identifier provided by the AC in the
> Join Response message differs from the WTP's
> currently running
> firmware version and the WTP has the requested image in its
> non-volatile memory, or if the WaitDTLS timer expires. This
> causes the WTP to initiate the DTLSShutdown command (see
> Section 2.3.2.1). This transition also occurs if the WTP
> receives one of the following DTLS notifications:
> DTLSAborted,
> DTLSReassemblyFailure or DTLSPeerDisconnect.
>
> AC: This state transition occurs either if the WaitJoin timer
> expires or if the AC transmits a Join Response message with a
> Result Code message element containing an error. This causes
> the AC to initiate the DTLSShutdown command (see
> Section 2.3.2.1). This transition also occurs if the AC
> receives one of the following DTLS notifications:
> DTLSAborted,
> DTLSReassemblyFailure or DTLSPeerDisconnect.
>
> Join to Image Data (m): This state transition is used by
> the WTP and
> the AC to download executable firmware.
>
> WTP: The WTP enters the Image Data state when it receives a
> successful Join Response message and determines and the
> included Image Identifier message element is not the same as
> its currently running image. The WTP also detects that the
> requested image version is not currently available
> in the WTP's
> non-volatile storage (see Section 9.1 for a full
> description of
> the firmware download process). The WTP initializes the
> EchoInterval timer (see Section 4.7), and transmits the Image
> Data Request message (see Section 9.1.1) requesting the start
> of the firmware download.
>
> AC: This state transition occurs when the AC receives the Image
> Data Request message from the WTP. The AC MUST transmit an
> Image Data Response message (see Section 9.1.2) to the WTP,
> which includes a portion of the firmware. The AC MUST start
> the ImageDataStartTimer timer (see Section 4.7).
>
> Join to Configure (n): This state transition is used by
> the WTP and
> the AC to exchange configuration information.
>
> WTP: The WTP enters the Configure state when it receives a
> successful Join Response, and determines that the included
> Image Identifier message element is the same as its currently
> running image. The WTP transmits the Configuration Status
> message (see Section 8.2) to the AC with message elements
> describing its current configuration. The WTP also
> starts the
> ResponseTimeout timer (see Section 4.7).
>
> AC: This state transition occurs immediately after the AC
> transmits the Join Response message to the WTP. If the AC
> receives the Configuration Status message from the
> WTP, the AC
> MUST transmit a Configuration Status Response message (see
> Section 8.3) to the WTP, and MAY include specific message
> elements to override the WTP's configuration. The AC also
> starts the ChangeStatePendingTimer timer (see Section 4.7).
>
> Configure to Reset (o): This state transition is used to reset the
> connection either due to an error during the
> configuration phase,
> or when the WTP determines it needs to reset in order
> for the new
> configuration to take effect.
>
> WTP: The WTP enters the Reset state when it receives a
> Configuration Status Response indicating an error or when it
> determines that a reset of the WTP is required, due to the
> characteristics of a new configuration.
>
> AC: The AC transitions to the Reset state when it receives a
> Change State Event message from the WTP that
> contains an error
> for which AC policy does not permit the WTP to
> provide service.
> This state transition also occurs when the AC
> ChangeStatePendingTimer timer expires.
>
> Configure to DTLS Teardown (p): This transition occurs when the
> configuration process aborts due to a DTLS error.
>
> WTP: The WTP enters this state when it receives one of the
> following DTLS notifications: DTLSAborted,
> DTLSReassemblyFailure or DTLSPeerDisconnect (see
> Section 2.3.2.2). The WTP MAY tear down the DTLS
> session if it
> receives frequent DTLSDecapFailure notifications.
>
> AC: The AC enters this state when it receives one of the
> following DTLS notifications: DTLSAborted,
> DTLSReassemblyFailure or DTLSPeerDisconnect (see
> Section 2.3.2.2). The WTP MAY tear down the DTLS
> session if it
> receives frequent DTLSDecapFailure notifications.
>
> Image Data to Image Data (q): The Image Data state is used by the
> WTP and the AC during the firmware download phase.
>
> WTP: The WTP enters the Image Data state when it receives an
> Image Data Response message indicating that the AC has more
> data to send.
>
> AC: This state transition occurs when the AC receives the Image
> Data Request message from the WTP while already in the Image
> Data state. The AC resets the ImageDataStartTimer timer.
>
> Image Data to Reset (r): This state transition is used to
> reset the
> DTLS connection prior to restarting the WTP after an image
> download.
>
> WTP: When an image download completes, the WTP enters the Reset
> state. The WTP MAY also transition to this state upon
> receiving an Image Data Response message from the AC (see
> Section 9.1.2) indicating a failure.
>
> AC: The AC enters the Reset state when an error occurs
> during the
> image download process or if the ImageDataStartTimer timer
> expires.
>
> Image Data to DTLS Teardown (s): This transition occurs when the
> firmware download process aborts due to a DTLS error.
>
> WTP: The WTP enters this state when it receives one of the
> following DTLS notifications: DTLSAborted,
> DTLSReassemblyFailure or DTLSPeerDisconnect (see
> Section 2.3.2.2). The WTP MAY tear down the DTLS
> session if it
> receives frequent DTLSDecapFailure notifications.
>
> AC: The AC enters this state when it receives one of the
> following DTLS notifications: DTLSAborted,
> DTLSReassemblyFailure or DTLSPeerDisconnect (see
> Section 2.3.2.2). The WTP MAY tear down the DTLS
> session if it
> receives frequent DTLSDecapFailure notifications.
>
> Configure to Data Check (t): This state transition occurs when the
> WTP and AC confirm the configuration.
>
> WTP: The WTP enters this state when it receives a successful
> Configuration Status Response message from the AC. The WTP
> initializes the EchoInterval timer (see Section 4.7), and
> transmits the Change State Event Request message (see
> Section 8.6).
>
> AC: This state transition occurs when the AC receives
> the Change
> State Event Request message (see Section 8.6) from the WTP.
> The AC responds with a Change State Event Response
> message (see
> Section 8.7). The AC MUST start the DataCheckTimer
> timer (see
> Section 4.7).
>
> Data Check to DTLS Teardown (u): This transition occurs
> when the WTP
> does not complete the Data Check exchange.
>
> WTP: This state transition occurs if the WTP does not
> receive the
> Change State Event Response before a CAPWAP transmission
> timeout occurs.
>
> AC: The AC enters this state when the DataCheckTimer timer
> expires (see Section 4.7).
>
> Data Check to Run (V): This state transition occurs when
> the linkage
> between the control and data channels has occured,
> causing the WTP
> and AC to enter their normal state of operation.
>
> WTP: The WTP enters this state when it receives a successful
> Change State Event Response message from the AC. The WTP
> initiates the data channel, which MAY require the
> establishment
> of a DTLS session, starts the DataChannelKeepAlive timer (see
> Section 4.7) and transmits a Data Channel Keep Alive packet
> (see Section 4.4.1). The WTP then starts the
> DataChannelDeadInterval timer (see Section 4.7).
>
> AC: This state transition occurs when the AC receives the Data
> Channel Keep Alive packet (see Section 4.4.1), with a Session
> ID message element matching that included by the WTP in the
> Join Request message. The AC disables the DataCheckTimer
> timer. Note that if AC policy is to require the data channel
> to be encrypted, this process would also require the
> establishment of a data channel DTLS session. Upon receiving
> the Data Channel Keep Alive packet, the AC transmits its own
> Data Channel Keep Alive packet.
>
> Run to DTLS Teardown (w): This state transition occurs
> when an error
> has occured in the DTLS stack, causing the DTLS session to be
> torndown.
>
> WTP: The WTP enters this state when it receives one of the
> following DTLS notifications: DTLSAborted,
> DTLSReassemblyFailure or DTLSPeerDisconnect (see
> Section 2.3.2.2). The WTP MAY tear down the DTLS
> session if it
> receives frequent DTLSDecapFailure notifications.
> The WTP also
> transitions to this state if the underlying reliable
> transport's RetransmitCount counter has reached the
> MaxRetransmit variable (see Section 4.7).
>
> AC: The AC enters this state when it receives one of the
> following DTLS notifications: DTLSAborted,
> DTLSReassemblyFailure or DTLSPeerDisconnect (see
> Section 2.3.2.2). The WTP MAY tear down the DTLS
> session if it
> receives frequent DTLSDecapFailure notifications. The AC
> transitions to this state if the underlying reliable
> transport's RetransmitCount counter has reached the
> MaxRetransmit variable (see Section 4.7).
>
> Run to Run (x): This is the normal state of operation.
>
> WTP: This is the WTP's normal state of operation.
> There are many
> events that result this state transition:
>
> Configuration Update: The WTP receives a
> Configuration Update
> Request message(see Section 8.4). The WTP MUST
> respond with
> a Configuration Update Response message (see Section 8.5).
>
> Change State Event: The WTP receives a Change State Event
> Response message, or determines that it must initiate a
> Change State Event Request message, as a result
> of a failure
> or change in the state of a radio.
>
> Echo Request: The WTP sends an Echo Request message
> (Section 7.1) or receives the corresponding Echo Response
> message, (see Section 7.2) from the AC.
>
> Clear Config Request: The WTP receives a Clear Configuration
> Request message (see Section 8.8). The WTP MUST reset its
> configuration back to manufacturer defaults.
>
> WTP Event: The WTP sends a WTP Event Request message,
> delivering information to the AC (see Section
> 9.4). The WTP
> receives a WTP Event Response message from the AC (see
> Section 9.5).
>
> Data Transfer: The WTP sends a Data Transfer Request message
> to the AC (see Section 9.6). The WTP receives a Data
> Transfer Response message from the AC (see Section 9.7).
>
> Station Configuration Request: The WTP receives a Station
> Configuration Request message (see Section 10.1), to which
> it MUST respond with a Station Configuration Response
> message (see Section 10.2).
>
> AC: This is the AC's normal state of operation:
>
> Configuration Update: The AC sends a Configuration Update
> Request message (see Section 8.4) to the WTP to update its
> configuration. The AC receives a Configuration Update
> Response message (see Section 8.5) from the WTP.
>
> Change State Event: The AC receives a Change State Event
> Request message (see Section 8.6), to which it
> MUST respond
> with the Change State Event Response message (see
> Section 8.7).
>
> Echo Request: The AC receives an Echo Request message (see
> Section 7.1), to which it MUST respond with an
> Echo Response
> message(see Section 7.2).
>
> Clear Config Response: The AC receives a Clear Configuration
> Response message from the WTP (see Section 8.9).
>
> WTP Event: The AC receives a WTP Event Request message from
> the WTP (see Section 9.4) and MUST generate a
> corresponding
> WTP Event Response message (see Section 9.5).
>
> Data Transfer: The AC receives a Data Transfer
> Request message
> from the WTP (see Section 9.6) and MUST generate a
> corresponding Data Transfer Response message (see
> Section 9.7).
>
> Station Configuration Request: The AC sends a Station
> Configuration Request message (see Section 10.1)
> or receives
> the corresponding Station Configuration Response message
> (see Section 10.2) from the WTP.
>
> Run to Reset (y): This state transition is used when either the AC
> or WTP tear down the connection. This may occur as
> part of normal
> operation, or due to error conditions.
>
> WTP: The WTP enters the Reset state when it receives a Reset
> Request message from the AC.
>
> AC: The AC enters the Reset state when it transmits a Reset
> Request message to the WTP.
>
> Reset to DTLS Teardown (z): This transition occurs when the CAPWAP
> reset is complete, to terminate the DTLS session.
>
> WTP: This state transition occurs when the WTP receives a Reset
> Response message. This causes the WTP to initiate the
> DTLSShutdown command (see Section 2.3.2.1).
>
> AC: This state transition occurs when the AC transmits a Reset
> Response message. The AC does not invoke the DTLSShutdown
> command (see Section 2.3.2.1).
>
> DTLS Teardown to Idle (8): This transition occurs when the DTLS
> session has been shutdown.
>
> WTP: This state transition occurs when the WTP has successfully
> cleaned up all resources associated with the control
> plane DTLS
> session. The data plane DTLS session is also
> shutdown, and all
> resources freed, if a DTLS session was established
> for the data
> plane. Any timers set for the current instance of the state
> machine are also cleared.
>
> AC: This is an invalid state transition for the AC.
>
> DTLS Teardown to Sulking (9): This transition occurs when repeated
> attempts to setup the DTLS connection have failed.
>
> WTP: The WTP enters this state when the
> FailedDTLSSessionCount or
> the FailedDTLSAuthFailCount counter reaches the value of the
> MaxFailedDTLSSessionRetry variable (see Section 4.8). Upon
> entering this state, the WTP MUST start the SilentInterval
> timer. While in the Sulking state, all received CAPWAP and
> DTLS protocol messages received MUST be ignored.
>
> AC: This is an invalid state transition for the AC.
>
> DTLS Teardown to Dead (~): This transition occurs when the DTLS
> session has been shutdown.
>
> WTP: This is an invalid state transition for the WTP.
>
> AC: This state transition occurs when the AC has successfully
> cleaned up all resources associated with the control
> plane DTLS
> session. The data plane DTLS session is also
> shutdown, and all
> resources freed, if a DTLS session was established
> for the data
> plane. Any timers set for the current instance of the state
> machine are also cleared. The AC's Service thread is
> terminated.
>
> 12.3. Discovery Attacks
> [...]
> Some implementations may wish to pass information about clients who
> have passed the discovery phase to the DTLS layer, authorizing only
> those clients to initiate a DTLS handshake. Note that the
> impact of
> this on mitigating denial of service attacks against the DTLS layer
> is minimal, because DTLS already uses client-side cookies
> to minimize
> processor consumption attacks. As a result, implementations SHOULD
> NOT maintain state between the discovery and DTLS
> handshake phases of
> the CAPWAP protocol initialization.
>
> </text>
>
> PatC
> -----Original Message-----
> From: Pat Calhoun (pacalhou)
> Sent: Tuesday, December 04, 2007 11:17 AM
> To: capwap
> Subject: [Capwap] Issue 30: Inconsistent state tracking on AC prior to
> DTLSEstablishment
>
> I wanted to provide a follow-up based on the conversation during the
> meeting yesterday. The issue that is being raised in this
> issue is that
> the state machine doesn't really work well on the AC. There
> is text that
> states that the AC has a different "state context" per WTP, but right
> now this would require that the AC maintains state during the
> discovery,
> etc. However, we have all agreed that the AC should not have to do so.
> So we agreed that we needed to provide more clarity on the
> state machine
> that allows for the AC to provide services such as responding to
> Discovery Requests, without explicitely maintaining per WTP state.
>
> I am working on modifications to the state machine, and expect to have
> this sent to the list later today.
>
> PatC
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-
Issue 30: Inconsistent state tracking on AC prior to DTLS Establishment Pat Calhoun (pacalhou), December 4 2007
-
Re: Issue 30: Inconsistent state tracking on AC prior to DTLSEstablishment Pat Calhoun (pacalhou), December 4 2007
- Re: Issue 30: Inconsistent state tracking on AC prior toDTLSEstablishment Scott Kelly, December 12 2007
- Re: Issue 30: Inconsistent state tracking on AC prior toDTLSEstablishment Pat Calhoun (pacalhou), December 13 2007
- Re: Issue 30: Inconsistent state tracking on AC prior toDTLSEstablishment Charles Clancy, December 15 2007
- Re: Issue 30: Inconsistent state tracking on AC prior toDTLSEstablishment Margaret Wasserman, December 15 2007
-
Re: Issue 30: Inconsistent state tracking on AC prior to DTLSEstablishment Pat Calhoun (pacalhou), December 4 2007
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